Hydraulic control system for vehicle automatic transmission

ABSTRACT

Disclosed is a hydraulic control system for an automatic transmission, including a hydraulic pump; a regulator valve for constantly regulating hydraulic pressure generated from said hydraulic pump; a reducing valve for reducing hydraulic pressure regulated by the regulator valve; a first-to-second speed shift valve for feeding hydraulic pressure to a friction member which is applied as a reacting element in a second speed; and a second-to-third/fourth-to-third speed shift valve for feeding hydraulic pressure to another friction member which is applied in third and fifth speeds. The first-to-second and second-to-third/fourth-to-third speed shift valves are respectively provided with control ports to which hydraulic pressure which is used for applying a friction member in fourth and fifth speeds is fed. The control ports are connected to a line, the line being provided with a shuttle valve.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a hydraulic control system for avehicle automatic transmission, whereby locking of a brake, which is areacting element, can be prevented during the shift operation between asecond speed to a fourth speed and responsiveness of the shift operationis improved.

2. Description of Related Art

In general, an automatic transmission provides a necessary gear ratio tooperate the vehicle under a wide range of speeds and loads. It does thiswith a minimum amount of effort on the part of the driver. That is,automatic upshifts and downshifts are a convenience for the driverbecause a foot-operated clutch is not required to shift gears, andbecause the vehicle can be brought to a stop without the use of a clutchand without shifting the transmission into neutral.

A conventional automatic transmission for a vehicle comprises a torqueconverter having an impeller, a turbine and a stator, a gear trainconnected to the torque converter to provide various forward speedranges and reverse, a plurality of friction members such as discclutches, one-way clutches which control gear action, and a hydrauliccontrol system for controlling the operation of the friction members.

The gear train is selectively operated by applying each friction memberas an input element, an output element or a reacting element. Theapplication or release of each friction member is performed in order.

However, if one friction member is applied before anotherpreviously-applied friction member is released, the gear train may bedamaged.

In addition, the gear train generally used a one-way clutch for reactingforce of a rotating member. The use of the one-way clutch makes the geartrain complicated.

SUMMARY OF THE INVENTION

Accordingly, it is the object of the present invention to provide ahydraulic control system for an automatic transmission to which a safetydevice is applied which can prevent the friction members from disorderlyoperation.

It is another object of the present invention to provide a hydrauliccontrol system for an automatic transmission which can simplify the geartrain and improve the responsiveness with respect to the shiftoperation.

Additional objects and advantages of the invention will be set forth inpart in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the invention. Theobjects and advantages of the invention will be realized and attained bymeans of the elements and combinations particularly pointed out in theappended claims.

To achieve the objects and in accordance with the purpose of theinvention, as embodied and broadly described herein, the inventionprovides a fail-safe device of a hydraulic control system for anautomatic transmission, comprising: a hydraulic pump; a regulator valvefor regulating hydraulic pressure generated from said hydraulic pumpconstant; a reducing valve for reducing hydraulic pressure regulated bythe regulator valve; a first-to-second speed shift valve for feedinghydraulic pressure to a friction member which is applied as a reactingelement in a second speed; and a second-to-third/fourth-to-third speedshift valve for feeding hydraulic pressure to another friction memberwhich is applied in third and fifth speeds; wherein the first-to-secondand second-to-third/fourth-to-third speed shift valves are respectivelyprovided with control ports to which hydraulic pressure which is usedfor applying a friction member in fourth and fifth speeds is fed; andthe control ports are connected to a line, said line being provided witha shuttle valve.

In another aspect, the present invention provides a fail-safety device,wherein the first-to-second speed shift valve includes a first valvespool and a first spring for biasing the first valve spool, and thesecond-to-third/fourth-to-third speed shift valve includes a secondvalve spool and a second spring for biasing the second valve spool, thecoefficient of elasticity of the first spring being larger than that ofthe second spring.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate one embodiment of the inventionand together with the description, serve to explain the principles ofthe invention.

FIG. 1 is a view showing a hydraulic control system of an automatictransmission according to a preferred embodiment of the presentinvention;

FIG. 2 is an enlarged view of the shift control part depicted in FIG. 1;

FIG. 3 is a schematic view showing a gear train which is controlled bythe hydraulic control system depicted in FIG. 1;

FIG. 4 is a table illustrating combination of friction members at eachspeed ratio in the automatic transmission according to the presentinvention, respectively; and

FIG. 5 is a table showing the operation status of the solenoid valvesused in the hydraulic control system shown in FIG. 1 for each mode.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Reference will now be made in detail to the present preferred embodimentof the invention, an example of which is illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

Certain terminology will be used in the following description forconvenience and reference only and will not be limiting. The words"right" and "left" will designate directions in the drawings to whichreference is made.

A preferred embodiment of the hydraulic control system according to thepresent invention is shown is FIG. 1. In FIG. 1, the control system isdepicted in a neutral state, or "N" range.

The hydraulic control system comprises a line pressure regulating part Afor converting hydraulic pressure fed from a hydraulic pump 2 intoconstant pressure, and a shift control part B for selectively feedinghydraulic pressure from the line pressure regulating part A to eachfriction member.

The line pressure regulating part A comprises a regulating valve 4 forregulating hydraulic pressure generated from the hydraulic pump 2constant, a reducing valve 6 for reducing hydraulic pressure from theregulating valve 4 to be lower than line pressure, and a torqueconverter control valve 10 and a damper clutch control valve 12 forcontrolling a damper clutch to improve power transmission efficiency.

The shift control part B comprises, as shown in FIG. 2, first to fourthpressure control valves 14, 16, 18 and 20, an N-D control valve 22, afirst-to-second speed shift valve 24, a second-to-third/fourth-to-thirdspeed shift valve 26, and a fourth-to-fifth speed shift valve 28.

The first to fourth pressure control valves 14, 16, 18 and 20 areconnected to the reducing valve 6 through a line 30 to thereby receivecontrol pressure therefrom. All of the pressure control valves have thesame structure as each other. That is, each pressure control valveincludes a spool groove 32, 34, 36 and 38, respectively and a valvespool 40, 42, 44 and 46, respectively.

Each valve spool 40, 42, 44 and 46 has a respective plug 56, 58, 60 and62, each of which is biased by a respective spring 48, 50, 52 and 54, arespective first land 64, 66, 68 and 70, which is integrally formed withthe respective plug, and a respective second land 72, 74, 76 and 78.

The spool groove 32 is provided with a first port 80 for receivinghydraulic pressure from a line 30, a second port 82 at or through whichhydraulic pressure is formed or released in accordance with theoperation of a first solenoid valve S1 which is On/Off controlled by atransmission control unit, a third port 84 for receiving line pressurefrom a line 31, and a fourth port 86 for feeding the line pressure tothe fourth-to-fifth speed shift valve 28 through a line 33.

Further, the spool groove 34 of the second pressure control valve 16 isprovided with a first port 88 for receiving hydraulic pressure from theline 30, a second port 90 at or through which hydraulic pressure isformed or released in accordance with the operation of a second solenoidvalve S2 which is also On/Off controlled by the transmission controlunit, a third port 92 for receiving line pressure from the line 31, afourth port 94 for feeding the line pressure to both the first-to-secondspeed shift valve 24 and the N-D control valve 22.

Further, the spool groove 36 of the third pressure control valve 18 isprovided with a first port 96 for receiving hydraulic pressure from theline 30, a second port 98 at or through which hydraulic pressure isformed or released in accordance with the operation of the thirdsolenoid valve S3 which is also On/Off controlled by a transmissioncontrol unit, a third port 100 for receiving line pressure from the line31, and a fourth port 102 for feeding the line pressure to thesecond-to-third/fourth-to-third speed shift valve 26 and thefourth-to-fifth speed shift valve 28 through the line 37.

Further, the spool groove 38 of the fourth pressure control valve 20 isprovided with a first port 104 for receiving hydraulic pressure from theline 30, a second port 106 at or through which hydraulic pressure isformed or released in accordance with the operation of a fourth solenoidvalve S4, a third port 108 for receiving line pressure from the line 31,and a fourth port 110 for feeding the line pressure to both thesecond-to-third/fourth-to-third speed shift valve 26 and thefirst-to-second speed shift valve 24.

The N-D control valve 22 is provided with a first port 112 communicatingwith the line 31 to directly receive hydraulic pressure therefrom and asecond port 114 for feeding hydraulic pressure coming through the firstport 112 to the first friction member B1.

The N-D control valve 22 is further provided with a third port 116 forreceiving hydraulic pressure from the second pressure control valve 16via a line 35. The first to third ports are varied in accordance withthe movement of a valve spool having a first land 118 and a second land122 biased by a spring 120.

The first-to-second shift valve 24 is provided with a first port 124connected to the second pressure control valve 16 via the line 35, andsecond port 126 connected to the third friction member B2 to feedapplication pressure thereto.

The first-to-second speed shift valve 24 is further provided with athird port 128 connected to third and fourth pressure control valves 18and 20 via lines 37 and 39, respectively, to thereby selectively receivecontrol pressure therefrom.

The first-to-second speed shift valve 24 includes a valve spool having afirst land 130 and a second land 134 biased by a spring 132.

The second-to-third/fourth-to-third speed shift valve 26 is providedwith a first port 136 connected to the third pressure control valve 18via the line 37 to thereby receive hydraulic pressure therefrom, asecond port 138 for feeding application pressure coming through thefirst port 136 to a fourth friction member B3, and a third port 140connected to the fourth pressure control valve 20 through the line 39 tothereby receive control pressure therefrom.

The second-to-third/fourth-to-third speed shift valve 26 includes avalve spool having a first land 142 and a second land 144 biased by aspring 141. The elastic force of the spring 141 is smaller than that ofthe spring 132 such that control can be carried out in turn by thehydraulic pressure.

The fourth-to-fifth speed shift valve 28 is provided with a first port146 receiving hydraulic pressure from the first pressure control valve14 through the line 33, a second port 148 for receiving applicationpressure from the third pressure control valve 18 through the line 37,and a third port 150 for feeding the application pressure to a fourthfriction member B3.

The fourth-to-fifth speed shift valve 28 includes a valve spool havingfirst and second lands 152 and 154.

Hydraulic pressure is directly fed from the fifth pressure control valve20 to a fifth friction member C2 through the line 39 at fourth and fifthspeeds of a drive mode or "D" range.

Accumulators 156, 158, 160 and 162 are respectively mounted on the linesconnected respectively to the second to fifth friction members C1, B2,B3 and C2. These accumulators temporally accumulate application pressurewhen the application pressure is fed to each friction member, such thatabrupt application of each friction member can be prevented, therebyaccomplishing the smooth shift operation.

The third port 128 of the first-to-second speed shift valve 24 isconnected to the second and third ports 138 and 140 of thesecond-to-third/fourth-to-third speed shift valve 26 through lines 91and 93, respectively. On a place where the lines 91 and 93 meet eachother, a shuttle valve 166 is disposed to feed hydraulic pressure fromone of the lines 91 and 93 to the third port 128 of the first-to-secondspeed shift valve 24.

Further, the second port 138 of the second-to-third/fourth-to-thirdspeed shift valve 26 and the third port 150 of the fourth-to-fifth speedshift valve 28 are designed to selectively feed hydraulic pressure tothe fourth friction member B3. The selective feeding of the hydraulicpressure is accomplished by a shuttle valve 167 which is mounted on aplace where the lines 95 and 97 meet.

The hydraulic control system as described above is used for controllinga gear train having more than one planetary gear as shown in FIG. 3.

Operation of the Hydraulic Control System

FIG. 4 illustrates the combination of friction members at each speedmode, and FIG. 5 charts the operation status of the solenoid valves foreach mode. The solenoid valves S1, S2 and S3 are types of normally openvalves and the solenoid valve S4 is a type of normally closed valve.

First Speed Operation of the "D" Range

In the shift operation of the first speed, hydraulic pressure generatedfrom the hydraulic pump 2 is fed to the first pressure control valve 14and the N-D control valve 22 via the manual valve MV along a line 31.

At this point, since the first and fourth solenoid valves S1 and S4 arecontrolled to OFF states according to a duty ratio by the transmissioncontrol unit as charted in FIG. 5, the valve spool of the first pressurecontrol valve 14 is displaced towards the right such that hydraulicpressure flowing along the line 31 flows to the line 33.

Accordingly, a portion of the hydraulic pressure within the line 33 isdirectly fed to the second friction member C1.

At this point, hydraulic pressure coming through the first port 112 ofthe N-D control valve 22 pushes the valve spool and is fed to the firstfriction member B1 through the second port 114, thereby accomplishingthe first speed.

By this hydraulic control operation, in the gear train, rotating powerof an input shaft X of the transmission is induced into a sun gear G1through the second friction member C2, and at this point, a ring gear G2operates as a reacting element by the application of the first frictionmember B1.

However, application pressure fed to the second friction member C1 istemporarily accumulated by the accumulator 156 so that the abruptapplication of the second friction member C1 can be prevented to therebyimprove the shift quality.

Second Speed Operation of the "D" Range

As the vehicle speed and the throttle opening increase, the transmissioncontrol unit starts to control the first, second, and fourth solenoidvalves S1, S2, and S4 to OFF states according to a duty ratio as chartedin FIG. 5. Accordingly, application pressure of the second frictionmember C1 maintains. However, since a portion of hydraulic pressurewithin the line 31 is fed as control pressure from the second pressurecontrol valve 16 to the third port 116 of the N-D control valve 22through the line 35, the valve spool of the N-D control valve 22 isdisplaced towards the left such that communication between the first andsecond port 112 and 114 of the N-D control valve 22 is disconnected.

Accordingly, hydraulic pressure which has been used as applicationpressure of the first friction member in the first speed is exhaustedthrough the exit port Ex.

Further, another portion of hydraulic pressure within the line 31 is fedto the first port 124 of the first-to-second speed shift valve 24 todisplace the valve spool thereof towards the right and is then fed tothe third friction member B2 through the second port 126.

That is, the first friction member B1 which has been applied in thefirst speed is released and the third friction member B2 is additionallyapplied with the second friction member C1, thereby accomplishing thesecond speed.

By this hydraulic control operation, in the gear train depicted in FIG.3, the friction member B1 which has been applied as a reacting elementis released and the friction member B2 is newly applied as a reactingelement to restrict a planet carrier K.

Third Speed Operation of the "D" Range

As the vehicle speed and the throttle opening increase further, thetransmission control unit starts to control the third solenoid valve S3to an OFF state in addition to the first, second, and fourth solenoidvalves S1, S2, and S4 according to a duty ratio as charted in FIG. 5.Accordingly, all of the valve spools of the first to fourth pressurecontrol valves are displaced towards the right.

By this operation, hydraulic pressure within the line 31 is fed to theN-D control, first-to-second speed shift, andsecond-to-third/fourth-to-third speed shift valves 22, 24 and 26 via thefirst to third pressure control valves 14, 16 and 18, and lines 33, 35and 37, respectively.

Accordingly, the second friction member C1 maintains its applicationstate. At this point, since control pressure is fed from the thirdpressure control valve 18 to the third port 128 of the first-to-secondspeed shift control valve 24 along the line 37, the valve spool of thefirst-to-second speed shift valve 24 is displaced towards the left suchthat communication of the first and second port 112 and 114 of thefirst-to-second speed shift valve 24 are disconnected.

Accordingly, supply of hydraulic pressure to the third friction memberB2 is interrupted, and at the same time, a portion of control pressureof the first-to-second speed shift valve is supplied to the fourthfriction member B3 along the line 91, thereby accomplishing the thirdspeed.

By this hydraulic control operation, in the gear train depicted in FIG.3, the fourth friction member B3 is applied as a reacting element torestrict the sun gear G3.

Fourth Speed Operation of the "D" Range

As the vehicle speed and the throttle opening increase further, thetransmission control unit starts to control only the fourth solenoidvalve S4 to an ON state to interrupt hydraulic pressure directed to theline 37.

By this operation, hydraulic pressure which has been directed to thefourth friction member B3 is disconnected and, at this point, hydraulicpressure within the line 31 is directed to the fifth friction member C2along the line 39 since the valve spool of the fourth pressure controlvalve 20 is displaced towards the left.

In other word, the second friction member C1 maintains its applicationstate and the friction member B3 is released. Further, the fifthfriction member C2 is applied to accomplish the fourth speed.

In this fourth speed state, there are two input elements (second andfifth friction members C1 and C2) without the reaction element.

Fifth Speed Operation of the "D" Range

As the vehicle speed and the throttle opening increase further, thetransmission control unit starts to control the first and fourthsolenoid valves S1 and S4 to ON states and the second and third solenoidvalves S2 and S3 to OFF states. Accordingly, the valves spools of thefirst and fourth pressure control valves are displaced towards the leftand the valve spools of the second and third pressure control valestowards the right.

By this operation, the fifth friction member C2 maintains itsapplication state, hydraulic pressure within the line 33 is interruptedby the first pressure control valve 14 such that the second frictionmember C1 which has been applied in the fifth speed is released.

Further, hydraulic pressure directing to the line from the thirdpressure control valve 18 is directed to the second and third ports 148and 150 of the fourth-to-fifth speed shift valve 28 and then fed to thefourth friction member B3 through the shuttle valve 167.

By this hydraulic control operation, in the gear train depicted in FIG.3, the fourth friction member B3 is applied as a reacting element torestrict the sun gear G3 and the planet carrier receives rotating forcefrom the input shaft X.

The hydraulic control system as described above has a fail-safe functionas a major feature of the present invention, which can prevent thefriction members from disorderly applying or releasing the shiftingoperation.

That is, in a shifting operation from second speed to third speed in thedrive "D" range, the second friction member C1 should be applied as aninput element and the fourth friction member B3 should be applied as areacting element. In this case, control pressure is directed to the line95 along the line 37 via the first and second ports 136 and 138 of thethird pressure control valve 18.

The control pressure is directed to the third port 134 of thefirst-to-second speed shift valve 24 via the shuttle valves 166 and 167to thereby displace the valve spool towards the left, therebydisconnecting the first and second ports with each other. As a result,hydraulic pressure which has been fed to the third friction member B2 isinterrupted as, at the same time, application pressure is fed to thefourth friction member B3.

Displacement of the valve spool of the first-to-second speed shift valve24 towards the left is for releasing the third friction member B2 whichhas been applied in the second speed. Application pressure for the thirdfriction member B2 is exhausted through the exit port Ex of thefirst-to-second speed shift valve 24.

In addition, when the speed ratio is changed from the third speed to thefourth speed, the second and fifth friction members C1 and C2 should besimultaneously applied and the fourth friction member B3 should bereleased.

To achieve this operation, the valve spool of thesecond-to-third/fourth-to-third speed shift valve 26 is displacedtowards the left by hydraulic pressure coming through the third port 140such that hydraulic pressure which has been fed to the fourth frictionmember B3 through the line 95 is interrupted.

At this point, control pressure is fed to the third port 128 of thefirst-to-second speed shift valve through the shuttle valve 166 againstthe application of the third friction member B2, such that the thirdfriction member B2 is not applied.

Further, when the speed ratio is changed from the fourth speed to thethird speed, control pressure for controlling the valve spools of thefirst-to-second and the second-to-third/fourth-to-third speed shiftvalves 24 and 26 is exhausted by releasing application pressure of thefifth friction member C2.

Accordingly, the third and fourth friction members B2 and B3 aresimultaneously applied. However, since the coefficient of elasticity ofthe spring 132 biasing the valve spool of the first-to-second speedshift valve 24 is larger than that of the spring 141 biasing the valvespool of the second-to-third/fourth-to-third speed shift valve 26, thevalve spool of the first-to-second speed shift valve 24 is displacedafter the valve spool of the second-to-third/fourth-to-third speed shiftvalve 26 is displaced, such that application of the third frictionmember B2 is prevented.

As described above, the fail-safe system of the hydraulic control systemcan prevent the friction members from disorderly applying by use of twoshift valves and one shuttle valve such that the breakdown of the geartrain can be prevented.

Further, the first-to-second speed shift valve and thesecond-to-third/fourth-to-third are operated in order by the springswhich have different coefficients of elasticity from each other, suchthat time control is possible and the interlock can be prevented.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the hydraulic control systemof the present invention and in the construction of this system withoutdeparting from the scope or spirit of the invention.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

What is claimed is:
 1. A hydraulic control system for an automatic transmission, comprising:a hydraulic pump; a regulator valve for regulating hydraulic pressure generated from said hydraulic pump constant; a reducing valve for reducing hydraulic pressure regulated by said regulator valve; a pressure control part including first to fourth pressure control valves which are controlled by first to fourth solenoid valves respectively, to independently simultaneously control a plurality of friction; members, wherein as a result of each respective control pressure from the pressure control valves, a respective friction member is applied or released; and a shift control part including an N-D control valve, a first-to-second speed shift valve, a second-to-third/fourth-to-third speed shift valve, and a fourth-to-fifth speed shift valve, all of which receive control pressure from the pressure control part, feed hydraulic pressure to the friction members and apply the friction members, wherein the first-to-second speed shift valve feeds hydraulic pressure to one of the friction members which is applied as a reacting element in a second speed, the second-to-third/fourth-to-third speed shift valve feeds hydraulic pressure to one of the friction members which is applied in third and fifth speeds, and the first-to-second and second-to-third/fourth-to-third speed shift valves are respectively provided with control ports to which hydraulic pressure, which is used for applying one of the friction members in fourth and fifth speeds, is fed for closing the respective speed shift valve.
 2. The hydraulic control system according to claim 1, wherein the control ports are connected to a line which is provided with a shuttle valve for feeding pressure which is used for applying the friction member which is applied in third or fifth speeds.
 3. The hydraulic control system according to claim 1, wherein said first-to-second speed shift valve includes a first valve spool and a first spring for biasing the first valve spool, and said second-to-third/fourth-to-third speed shift valve includes a second valve spool and a second spring for biasing the second valve spool, the coefficient of elasticity of said first spring being larger than that of said second spring.
 4. A hydraulic control system for an automatic transmission, comprising:a hydraulic pump; a regulator valve for regulating hydraulic pressure generated from said hydraulic pump constant; a reducing valve for reducing hydraulic pressure regulated by said regulator valve; a pressure control part including first to fourth pressure control valves which are controlled by first to fourth solenoid valves, respectively, to independently simultaneously control a plurality of friction members for application or release; and a shift control part including an N-D control valve, a first-to-second speed shift valve, a second-to-third/fourth-to-third speed shift valve, and a fourth-to-fifth speed shift valve, all of which receive control pressure from the pressure control part and feed hydraulic pressure to the friction members; wherein the first-to-second and second-to-third/fourth-to-third speed shift valves are respectively provided with control ports to which hydraulic pressure, which is used for applying a friction member in fourth and fifth speeds, is fed, and wherein the control ports are connected to a line which is provided with a shuttle valve.
 5. A hydraulic control system for an automatic transmission, comprising:a hydraulic pump; a regulator valve for regulating hydraulic pressure generated from said hydraulic pump constant; a reducing valve for reducing hydraulic pressure regulated by said regulator valve; a pressure control part including first to fourth pressure control valves which are controlled by first to fourth solenoid valves, respectively, to independently simultaneously control a plurality of friction members for application or release; and a shift control part including an N-D control valve, a first-to-second speed shift valve, a second-to-third/fourth-to-third speed shift valve, and a fourth-to-fifth speed shift valve, all of which receive control pressure from the pressure control part and feed hydraulic pressure to the friction members; wherein said first-to-second speed shift valve includes a first valve spool and a first spring for biasing the first valve spool, and said second-to-third/fourth-to-third speed shift valve includes a second valve spool and a second spring for biasing the second valve spool, the coefficient of elasticity of said first spring being larger than that of said second spring. 